1. Field of the Invention
The present invention relates to resource scheduling. More particularly, the present invention relates to a terminal and resource scheduling thereof for transmitting an ACKnowledgement (ACK) corresponding to data received from a base station.
2. Description of the Related Art
Transmission Control Protocol (TCP) has been developed to efficiently use limited bandwidth by adjusting a transmission rate of a sender and prevent a network from being overloaded. In TCP, the sender checks a Round Trip Time (RTT) based on a Packet Sequence Number (PSN) of the transferred packet and an ACKnowledgement (ACK) received in response to the packet. The sender increases the size of a congestion window to increment a number of packets using congestion control techniques such as slow start and congestion avoidance for a low network congestion situation. However, when a router experiences high network congestion and thus packet loss occurs, the sender decreases the size of the congestion window to reduce the transmission rate using techniques such as time-out and window halving.
Since TCP is designed for a wired network environment, it causes performance degradation to adopt TCP to a wireless communication environment without consideration of the characteristics of the wireless communication. In the wired communication environment, the packet loss caused by a packet error or a router buffer overflow is the main reason for the time-out or window halving. However, in a case where a wireless network is added to an end-user node, the resource distribution for sharing limited resources among multiple terminals increases the latency as compared to the wired network environment. If the channel condition gets worse, it may not be possible to transmit a large amount of data, regardless of the resource distribution.
In this case, although no packet loss has actually occurred, the delay spike in the wireless environment causes an unnecessary time-out (i.e., spurious time-out). That is, although the ACK arrives at the base station with long RTT, the sender makes a time-out decision so as to unnecessarily reduce the size of the congestion window. Although it may be controlled partially with the basic function of TCP, the probability of the spurious time-out increases significantly when the terminal's mobility or channel fluctuation increases.